I'm writing to get some advice. I previously had a board failure in my SSE and completed repair by building a new board that has now been in service for 1 year, 3 months. At the time of the rebuild, I acquired a new set of Tung Sol (Russia) 6550 tubes. The amp uses a set of Edcor transformers (Power and CXSE outputs).
Tonight I was using the amplifier and afterward it sat idle for a little bit. Just as I was going to switch it off, I heard a large bang which got me running and to the amp quickly, followed by an odor when I was nearby. I shut the power down, noticing that there was a mild glow at the seams of the plate on the right power tube.
Inspecting the amplifier, I found C12 blown off the board and slightly bulged at the top. It appears it may have leaked an amount of electrolyte onto the bottom cover below. Obviously, the capacitor is shot, but I'm at a loss as to what happened. Everything else that I can see so far looks to be fine. The installed parts (on both channels) are Nichicon 1500uF 63V rated 105C.
Is there any diagnostic testing I should do before or after replacing the capacitor? I'm using the 560 ohm cathode resistors, is there a problem with them and the 6550?
The only other time I've seen this problem is when I tried using some vintage 6550's, but in this case the tubes have been running fine for over a year, so I'm trying to figure out if I'm pushing them too hard, or what else might be at fault.
Thanks for any input!
Tonight I was using the amplifier and afterward it sat idle for a little bit. Just as I was going to switch it off, I heard a large bang which got me running and to the amp quickly, followed by an odor when I was nearby. I shut the power down, noticing that there was a mild glow at the seams of the plate on the right power tube.
Inspecting the amplifier, I found C12 blown off the board and slightly bulged at the top. It appears it may have leaked an amount of electrolyte onto the bottom cover below. Obviously, the capacitor is shot, but I'm at a loss as to what happened. Everything else that I can see so far looks to be fine. The installed parts (on both channels) are Nichicon 1500uF 63V rated 105C.
Is there any diagnostic testing I should do before or after replacing the capacitor? I'm using the 560 ohm cathode resistors, is there a problem with them and the 6550?
The only other time I've seen this problem is when I tried using some vintage 6550's, but in this case the tubes have been running fine for over a year, so I'm trying to figure out if I'm pushing them too hard, or what else might be at fault.
Thanks for any input!
The resistor did not fail, though it may have drifted in value, if that is possible? When I installed the resistors I chose a pair that were very close (all of the lot I received were quite close anyhow. The side that is normal measures 556 ohms, like those in the spares bag. The side where the cap blew measures 595 ohms. That falls within the 10% tolerance for 560, and if anything should have that channel at a slightly lower bias point.
One thing I should note is that the amplifier was accidentally switched on and off within a few seconds a few days prior by an outlet controller. There was a bit of a thunk, but upon inspection everything looked and ran fine, so I figured it was probably OK. Not sure if that could somehow stress just that one capacitor, but thought it was worth mention.
I've had this happen twice. The culprit was a bad tube with a grid to cathode short that developed after being in use for several hours. The tubes had previously ran fine for over a year. I didn't catch mine quick enough and also blew the cathode resistor.
I would replace both the resistor and the cap, and as long as you have it apart, you might as well do it for both channels.
-Phil
I would replace both the resistor and the cap, and as long as you have it apart, you might as well do it for both channels.
-Phil
Those white ceramic resistors are usually hard to kill. I have seen a bad tube blow the cap without taking out the resistor.
The usual culprit here is the tube. Most new production tubes have less than stellar vacuum quality and metal purity. As time goes by more and more ions are outgassed from the internal elements due to heat. These ions form a conductive path in the vacuum which caused grid current and upsets the bias. Over time this grid current will get worse until the tube eventually goes into red plate runaway. Often there is a tell tale pale blue or purple glow inside the plate area which is ionization.
A deep blue glow on the inside surface of the glass itself is not a problem and is usually the sign of a good vacuum.
In this case I would replace the cap, resistor and output tube. Clean as much of the goo off the board as possible with alcohol. Lacquer thinner or other strong solvents will attack the white silkscreen and maybe even the green solder mask.
George,
Thanks for weighing in - I went back to check my records and it turns out that the pair of tubes is less than a year old! Can anyone comment on whether I should consider other tubes for use instead? How long is everyone seeing a pair of output tubes last in the SSE these days? This amp is used almost daily. Now I'm wondering if I should be preventative and replace the tube that was on the channel that is still fine.
I have another pair of TS 6550's that I bought used to see if I liked them, and they lasted much longer than this, but I wonder if they caused the damage to my previous PCB in the same failure fashion when the board was scorched by the bias resistor. Seems like that could have been a runaway as well. The irony is it seems that the right channel is always the one affected. The left tube of that set wasn't having any problems at the time of that failure either.
It looks like following your advice has paid off, as the board has no indication of heat damage this time (I put the resistors on the top of the board and put thermal compound between them and the thick top aluminum plate.
Does the seller of the tubes matter when purchasing new production stock? Are there different grades or are they just all poorly made? My first pair of tubes were New Sensor Electro-Harmonix KT-88's and they lasted many (3-5?) years. I think the one had a vacuum failure, and the other was still fine but I switched to a different style to try something else.
I take it that these type of slow failures within the tube won't show any evidence on a tester either? Is there anything that can be done with the circuit or meters to monitor tube life more closely and prevent amp damage? I'd consider installing current meters if they would be helpful. It is a lot easier to replace a tube than to have to take the whole amp apart to repair after a catastrophic failure!
Thankfully there wasn't too much goo released, so I've already got the cleanup under control. I have one capacitor left, so I'll have to pick up some spares on my next parts order.
I did some testing tonight after replacing the right channel capacitor and resistor, along with trying some other tubes to see where their voltage values ran. The resistance value is within 1 ohm of the left channel, so it should be negligible safe for the tubes.
The big motor capacitor (B+) measures 452V. At that time, I measured 49V across the left tube's resistor (was operating fine) and 59V across the right channel tube, which if I calculate right says that the right tube is drawing along the lines of 20% more current as compared to the left. Both tubes have only the deep blue glow on the glass, nothing indicating ionization inside the plate, nor any redness on any part of the plate. These were taken after a decent warmup time, but not an extended runtime.
I'm not extensively versed on the ins and outs of tube circuit design, but from using the tube data sheet at zero signal it appears that the current being drawn at idle may be higher than ideal in the right tube (and possibly nominal or slightly above in the left).
Either way, switching the tubes between channels results in the voltages being more or less identical, just on the opposite side as would be expected. So I suspect that the circuit behavior is solely based on the tubes being used and that nothing else appears to be damaged.
Switching to the other pair of TS 6550 tubes from the prior PCB yields both channels with higher voltages (and currents) across the cathode resistors.
So, to those with more knowledge - are there other circuit measurements that would be helpful for me to take? Is there an issue with one or more tubes, and/or the choice of cathode resistor given these values?
I'm just trying to understand where I am and what I should do from here for the best reliability. Thanks so much for all of the feedback!
The big motor capacitor (B+) measures 452V. At that time, I measured 49V across the left tube's resistor (was operating fine) and 59V across the right channel tube, which if I calculate right says that the right tube is drawing along the lines of 20% more current as compared to the left. Both tubes have only the deep blue glow on the glass, nothing indicating ionization inside the plate, nor any redness on any part of the plate. These were taken after a decent warmup time, but not an extended runtime.
I'm not extensively versed on the ins and outs of tube circuit design, but from using the tube data sheet at zero signal it appears that the current being drawn at idle may be higher than ideal in the right tube (and possibly nominal or slightly above in the left).
Either way, switching the tubes between channels results in the voltages being more or less identical, just on the opposite side as would be expected. So I suspect that the circuit behavior is solely based on the tubes being used and that nothing else appears to be damaged.
Switching to the other pair of TS 6550 tubes from the prior PCB yields both channels with higher voltages (and currents) across the cathode resistors.
So, to those with more knowledge - are there other circuit measurements that would be helpful for me to take? Is there an issue with one or more tubes, and/or the choice of cathode resistor given these values?
I'm just trying to understand where I am and what I should do from here for the best reliability. Thanks so much for all of the feedback!
There have been a few cases where a leaky coupling cap has caused a similar meltdown. In all cases they were expensive boutique caps.
to test them, pull the output tubes and the 12AT7. Stick a voltmeter between ground and the grid pin on the 6550. Set the meter on 600 volts or whatever it's highest range is. Turn the amp on. The voltmeter should read a large positive voltage, then slowly drop toward zero. It MUST eventually reach zero, usually within a minute or two. A positive voltage on the grid pin of an output tube will cause it to draw excessive current.
The Grid (1) pin shows a small amount of voltage which very quickly goes to zero upon power up. This is true on both channels of the amplifier. I'm using AuriCaps XO as the coupling capacitors.
I ran the amplifier again for a short period of time, with a different tube in the right position. There is some red glow along the seams of the plate after 5-10 minutes, which I suspect indicates something wrong, so I shut it down. I did not see any purple/blue glow inside the plate.
Anything else I should test here?
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Thought I'd post an update, I've played a game of musical-tubes here and have gotten to thinking that Occam's Razor applies here after all. George's suggestion (bad tubes) seems to be on point. It might be worth noting that I don't see any blue/purple glow inside the plate but more than one of these tubes gets just the slightest red plate glow after 10-20 minutes tops. The problems follow when moving them between channels. I'm just surprised they were so short-lived. I've also had a new production TS 5AR4 fail due to having internal arcing.
When I swapped the newer left channel tube into the right socket, it works beautifully and doesn't show any red plate after extended operation, ruling out any other component issues on that side.
Under very careful and close observation, all of the three other tubes in my possession slowly and just slightly glow red at the seam no matter what channel they are installed in, so likely they are just all gassy.
In light of this, I have two questions:
1. Is anyone else running the new production TS 6550 and what bias point are you using? I believe the Edcor PT I use may run a little bit hotter than some of the others in use, so I'm curious how hard your amp pushes these and if maybe that is factoring into their shorter life?
2. Can anyone comment on what brand and model of tubes have given the best sound/life combination in their SSE? I've liked the TS 6550 but have wondered if the KT120 or another model might fare better here (and if there is any reason not to use them, too).
3. Does the supplier where the tubes get purchased matter? I had better luck with my first set EH KT88 that came from TubeDepot. These newer ones came from *Bay sellers. FWIW, I emailed the seller and they did offer to replace the bad tube even though usually they only guarantee 90 days.
When I swapped the newer left channel tube into the right socket, it works beautifully and doesn't show any red plate after extended operation, ruling out any other component issues on that side.
Under very careful and close observation, all of the three other tubes in my possession slowly and just slightly glow red at the seam no matter what channel they are installed in, so likely they are just all gassy.
In light of this, I have two questions:
1. Is anyone else running the new production TS 6550 and what bias point are you using? I believe the Edcor PT I use may run a little bit hotter than some of the others in use, so I'm curious how hard your amp pushes these and if maybe that is factoring into their shorter life?
2. Can anyone comment on what brand and model of tubes have given the best sound/life combination in their SSE? I've liked the TS 6550 but have wondered if the KT120 or another model might fare better here (and if there is any reason not to use them, too).
3. Does the supplier where the tubes get purchased matter? I had better luck with my first set EH KT88 that came from TubeDepot. These newer ones came from *Bay sellers. FWIW, I emailed the seller and they did offer to replace the bad tube even though usually they only guarantee 90 days.
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My TSE ran for nearly 2 years as the amp for my PC speakers. It was on whenever the PC was on, which was pretty much whenever I was home whether I was using it or not. It still has the same set of tubes in it which are now over 10 years old.....they are EH KT88's from Tube Depot.
Normally I look for cheap tubes since I tend to abuse them, and these were no exception. About 10 to 12 years ago a popular tube seller shows me a box full of Russian tubes. The story was that they were "lightly used" or "previously auditioned" at a "trade show." My guess is that they were customer returns. Either way there were lots of EL34's, KT88's, 6550's, 5881's and 6L6GC's. All had Tube Depot stickers on them, and they were $10 each. How could I say no. 4 of the EH EL34's were immediately stuck into a 100 watt Marshall guitar amp where they worked fine. A pair of the KT88's went into my TSE, and some of the others got used in various amps. All have lived long lives, except one that I blew up by accident.
Tube Depot and other quality resellers get tubes by the hundreds directly from the importer and grade them out. The good ones get stickers, and the not so good ones go to the Ebay sellers.
Many years ago AES was hawking some Chinese "Coke Bottle 6L6GC's" for about $8 with the statement, "we couldn't blow these up" so I got some and accepted the challenge....I did blow some of them up, but they took some serious abuse. Later I found the same tubes on Ebay for $4 each, and they ALL blew up rather easily.
I'm guessing that your amp may be running a bit hotter than other people's. Maybe your power transformer is a bit higher output than others, and maybe your line voltage is high. Either way cathode voltages near 60 volts is too much.
What voltage do you get with a tube that doesn't show red? 59 volts across a 560 ohm resistor is 105 mA. That's over 41 watts of dissipation in the tube, and that will bring out the redness. 49 volts is 87 mA which is still a bit high, but it's 35 watts of plate dissipation.
George,
Thanks so much for sticking with me here! I am running Edcor's XPWR033 transformer, which is rated for: 120V, 60Hz. line to 760V (380-0-380) at 200mA center tapped, 6.3V at 5A and 5V at 3A. Output transformers are Edcor's CXSE25-8-5K. I'm also using the Triad C-14X (under chassis) Choke and a Motor Run Capacitor.
Since I've had a few issues here and there since that first pair of tubes, I suspected that I've gotten some lesser quality tubes AND that my amp may be running things a bit hot. Obviously I haven't had any major failures aside that resistor burn on the old board and I've been running the amp for about 10 years now, but I've had many more pairs of tubes than you! If the current pair flaked after a year, I'm guessing the hard life and the less than ideal characteristics of modern tubes played a part.
Ironically, only one of my original Tube Depot KT88's failed, I still have the other which was working fine.
I bought up a few pairs of those 6L6GCs when you were talking about them, as I figured they would be good tubes for burn-in testing, can't remember offhand where I made the purchase but some were better than others.
I'll have to take some more measurements from different tubes. Some of those 6L6GC's and also some KT88's are around here. I believe the good tube that was stable without any red was running at 49V. If there are any other pertinent measurements that might help sort things out, I'd be happy to take them as well.
It is probably worth mentioning I have a few NOS 6550's too, but I think I read at some point that they bias differently than the new ones.
Thanks so much for sticking with me here! I am running Edcor's XPWR033 transformer, which is rated for: 120V, 60Hz. line to 760V (380-0-380) at 200mA center tapped, 6.3V at 5A and 5V at 3A. Output transformers are Edcor's CXSE25-8-5K. I'm also using the Triad C-14X (under chassis) Choke and a Motor Run Capacitor.
Since I've had a few issues here and there since that first pair of tubes, I suspected that I've gotten some lesser quality tubes AND that my amp may be running things a bit hot. Obviously I haven't had any major failures aside that resistor burn on the old board and I've been running the amp for about 10 years now, but I've had many more pairs of tubes than you! If the current pair flaked after a year, I'm guessing the hard life and the less than ideal characteristics of modern tubes played a part.
Ironically, only one of my original Tube Depot KT88's failed, I still have the other which was working fine.
I bought up a few pairs of those 6L6GCs when you were talking about them, as I figured they would be good tubes for burn-in testing, can't remember offhand where I made the purchase but some were better than others.
I'll have to take some more measurements from different tubes. Some of those 6L6GC's and also some KT88's are around here. I believe the good tube that was stable without any red was running at 49V. If there are any other pertinent measurements that might help sort things out, I'd be happy to take them as well.
It is probably worth mentioning I have a few NOS 6550's too, but I think I read at some point that they bias differently than the new ones.
Time for a bit of an update. I received a new tube to replace the one that was drawing excessive current, the seller replaced it for free which was respectable. Measurements for that new tube are on the Right channel. The Left is the original tube that was operating before the failure.
Plate Voltage 458V
Bias Resistor Voltage After warming up, at idle:
Left: 57V
Right: 46V
Worth note: The left channel voltage has crept up slightly with the amp the longer it idles, as it started around 49V (delta of 8V). The right channel voltage seems to drift less at 46V. I believe it started at 42-43V, so only 4V drift. Is the greater change potentially indication of a older or failing tube, or just simply variation as the tube warms up?
A cathode bias calculator appears to show that the left tube is 39W plate dissipation and 97 mA plate current, where the right is 32W and 78 mA based on the measurements I took above.
Voltage Coupling Cap Positive to Ground:
Left: 209V
Right: 199V
Are there any other measurements of significance I should take? Any other thoughts at this time?
If these tubes are indeed failing prematurely, would bias meters be useful to help keep an eye on the tubes as they age and indicate time for replacement? Should the bias resistor values be changed due to the operating point of the amp that I've measured with these tubes?
Thanks so much for the input! I'm going to try and swap the PSVANE KT88-TII tubes in once these cool and I can give some operating voltages for them as well.
Plate Voltage 458V
Bias Resistor Voltage After warming up, at idle:
Left: 57V
Right: 46V
Worth note: The left channel voltage has crept up slightly with the amp the longer it idles, as it started around 49V (delta of 8V). The right channel voltage seems to drift less at 46V. I believe it started at 42-43V, so only 4V drift. Is the greater change potentially indication of a older or failing tube, or just simply variation as the tube warms up?
A cathode bias calculator appears to show that the left tube is 39W plate dissipation and 97 mA plate current, where the right is 32W and 78 mA based on the measurements I took above.
Voltage Coupling Cap Positive to Ground:
Left: 209V
Right: 199V
Are there any other measurements of significance I should take? Any other thoughts at this time?
If these tubes are indeed failing prematurely, would bias meters be useful to help keep an eye on the tubes as they age and indicate time for replacement? Should the bias resistor values be changed due to the operating point of the amp that I've measured with these tubes?
Thanks so much for the input! I'm going to try and swap the PSVANE KT88-TII tubes in once these cool and I can give some operating voltages for them as well.
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PSVANE KT88-TII
Plate Voltage 457V
Bias Resistor Voltage After some warm up, at idle:
Left: 46V
Right: 46V
A cathode bias calculator appears to show that the both tubes have 32W plate dissipation and 78 mA plate current.
Voltage Coupling Cap Positive to Ground:
Left: 208V
Right: 199V
It appears these tubes have a much closer operating point than the Tung Sol's, but again they are similar in age versus the TS pair, where one is new and the other a year old. The PSVANE were also measured for 60 mA and 65 mA plate current on their testing.
Hopefully this helps a bit more than just the measurements from the TS pair of tubes.
Plate Voltage 457V
Bias Resistor Voltage After some warm up, at idle:
Left: 46V
Right: 46V
A cathode bias calculator appears to show that the both tubes have 32W plate dissipation and 78 mA plate current.
Voltage Coupling Cap Positive to Ground:
Left: 208V
Right: 199V
It appears these tubes have a much closer operating point than the Tung Sol's, but again they are similar in age versus the TS pair, where one is new and the other a year old. The PSVANE were also measured for 60 mA and 65 mA plate current on their testing.
Hopefully this helps a bit more than just the measurements from the TS pair of tubes.
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Off the top of my head, out of the new production tubes I have used, and sometimes abused, in the SSE:
JJ 6V6S - tough as nails, and sounded good, gave all of them to my nephew the guitar player.
Sino 6V6 - seem tough, sound about average - have them in a modded Elekit TU-879S at the lake house, as my wife tends to forget to turn it off - for weeks or months at a time ... Hard to find.
EH 6V6 - little better than junk in my opinion, half of the ones I've had went crackly early in their life. Sounded OK when they worked. Which wasn't for long.
TS 6L6STR - the ones I had took almost 500 volts plate to cathode with no sign of distress. Seemed well built. A nice looking tube, imo. Don't recall much more about them. Gave all of them to my nephew the guitar player.
TS 6L6G - look terrific, half of the ones I've had spontaneously went to air sitting in their boxes; the other half have given excellent service and look and sound really good. I expect the innards of this tube are the same as the 6L6STR. Expensive.
TS 5881 - seems fine, sounds good, looks well built, the pair I have have given good service. Reasonable price. Unlike the 6550, it is not an insult to Tung Sol 5881's to call these a Tung Sol 5881.
Sino Coke Bottle 6L6GC - tough as nails, look good, sound okay to me, no longer available as far as I know. Gave some to my nephew the guitar player, kept a small stash for myself.
Sino straight bottle 6L6GC - haven't used them for hi fi. I do use them as pass tubes in high voltage power supplies and they seem OK in this application, but I lost about 10 volts compared to RCA blackplates in one power supply, so their internal resistance may be a bit high, or something else is a bit off. Seem like a good value.
Sovtek 6L6GB - they call it something else now. Works fine as a 6L6GB.
JSC Svetlana ( Winged C ) 6L6GC. Terrific. Near or completely unobtainium now, unfortunately.
Groove Tubes new production USA made 6L6GE - look great, work great, sound great, but I'm afraid to use them because they are unobtainium now. Haven't tried the Chinese made version.
JJ EL34 - blue glass, sound good, about a 33% early mortality rate. I've never had a problem with undersized pins on a JJ tube, although some folks complain about that.
Sino EL34 - tough, don't sound that great to me, but tough and cheap.
JSC Svetlana EL34 - Mine have given good service life, not sure they are as great as all the hype. Maybe I'm not an EL34 person.
Russian Mullard EL34 - don't recall that much about them, so I guess they were OK - gave them all to my nephew the guitar player.
Groove Tubes new USA production GE 6CA7 - 50% failure rate. The ones that worked, worked well. Looked good, though. Unobtainium now and just as well.
Ei 6CA7 - used sparingly, sound good, tough, thick, glass bulb, now unobtainium, unfortunately.
TS6550 - probably junk, the ones I kept seem to dissipate the getter fast. Sounded mediocre, but look good. Gave most of them to my guitar playing nephew. Nothing in common with a real Tung Sol 6550 in my opinion.
JSC Svetlana 6550C - terrific, almost, or as good as, real 6550's, unobtainium now.
Early first generation Sino KT-88 - never a dull moment here, but the ones that work, work pretty well.
JSC Svetlana KT-88 - Terrific, gave most of them to my nephew the guitar player. Probably made a mistake there. Unobtainium now.
Sovtek KT-88 - seem fine for a cheap tube.
Sino 6146B. Work good for AF, sound good. Seem to have more plate dissipation than US made 6146B, and have a visible heater. Service life not comparable to US made tubes, and they have squared off, rather than tapered, pins. Haven't tried them for RF and likely never will because of the pins.
Sino 5AR4 - junk.
Sovtek 5AR4 - Okay, I've had some fail.
Sovtek 5Y3GT - Not a 5Y3GT, not even close, look nice, but are fragile. All of mine have failed. They do look nice, though.
There may be some others, but that's what I recall off the top of my head. I have quite a few other new production tubes, but I have so many old U.S. made tubes that I don't fool with the new stuff much. I haven't found any difference in reliability between reputable sellers and eBay sellers. When I get a bad one, I just suck it up and move on.
Win W5JAG
Win, Thanks for the large amount of commentary and information. I'm curious, on the 6550's as the getter dissipates (mine did this too) does the bias point start to drift? The attached photo is a new tube and the one that is about 10 months old. Do you think other Russian tubes (Sovtek, etc) are similar or do the TS 6550's have an issue unique to them?
I'm trying to figure out if the tube pair I got both had a poor vacuum to start with or some other flaw. I might have to check with the seller again, since now what was the "better" tube looks bad by comparison to both my set of used KT-88's and my new 6550, and looks like it too will run away.
The KT-88's have a great sound, but they are the most pricey set I've owned and I had problems with them too! I had to be sent a new set because one failed and lost vacuum, and then one of the new set appears to also run too hot. Between one old and one new, I have a stable set of tubes!
I'm also curious if the bias point (or B+ level) is playing a part, or if the tubes alone are causing the problems I've seen. I know if I am running them too hot, they'll have a reduced lifespan. The TS data sheet (if it is to be trusted as fact) claims 42 W max dissipation. I can't imagine running the left channel at 92% will bode well for long. The new tube is at 76% of max dissipation, that seems more reasonable.
From the data I can find on the KT-88's it appears that they have a bit more headroom on their max values. Maybe this is part of why I've historically fared better with them vs the 6550's, since I'm gathering that less stress will ensure a longer life.
Can anyone comment on the "bias point" ratings, like Tube Depot sells? Is it better to pick tubes at one end or the other of this range?
Thanks again for all the input, hopefully I'll get to the point where I can get some reliable tubes and enjoy the amp mostly trouble free and with peace of mind!
I'm trying to figure out if the tube pair I got both had a poor vacuum to start with or some other flaw. I might have to check with the seller again, since now what was the "better" tube looks bad by comparison to both my set of used KT-88's and my new 6550, and looks like it too will run away.
The KT-88's have a great sound, but they are the most pricey set I've owned and I had problems with them too! I had to be sent a new set because one failed and lost vacuum, and then one of the new set appears to also run too hot. Between one old and one new, I have a stable set of tubes!
I'm also curious if the bias point (or B+ level) is playing a part, or if the tubes alone are causing the problems I've seen. I know if I am running them too hot, they'll have a reduced lifespan. The TS data sheet (if it is to be trusted as fact) claims 42 W max dissipation. I can't imagine running the left channel at 92% will bode well for long. The new tube is at 76% of max dissipation, that seems more reasonable.
From the data I can find on the KT-88's it appears that they have a bit more headroom on their max values. Maybe this is part of why I've historically fared better with them vs the 6550's, since I'm gathering that less stress will ensure a longer life.
Can anyone comment on the "bias point" ratings, like Tube Depot sells? Is it better to pick tubes at one end or the other of this range?
Thanks again for all the input, hopefully I'll get to the point where I can get some reliable tubes and enjoy the amp mostly trouble free and with peace of mind!
Attachments
I haven't seen other Russian tubes do this, and I have read more than one complaint about the new TS 6550 in this regard. In fairness, they have plenty of getter to start with, so other than appearance, which is important now a days as the tubes are usually on display, this is probably a non issue.
I don't recall the bias drifting on mine, or the tubes going into runaway, but I doubt I ran them at more than 35 watts or so. I haven't used them in years. I don't know if there is a datasheet for the "new" TS 6550, but the real TS 6550 specs a max grid resistor of 250K for cathode bias, and the SSE is stock at 220K. You could try lowering your grid resistor value some to see if it stops the run away, or improves the tube performance, if you are inclined to tinkering with things.
I like the TS 6L6G but they are expensive, doubly so when half fail just sitting in the box ...
I don't know anything about Tube Depots bias point ratings. Without knowing how they get this data point, it seems rather meaningless.
Win W5JAG
I don't recall the bias drifting on mine, or the tubes going into runaway, but I doubt I ran them at more than 35 watts or so. I haven't used them in years. I don't know if there is a datasheet for the "new" TS 6550, but the real TS 6550 specs a max grid resistor of 250K for cathode bias, and the SSE is stock at 220K. You could try lowering your grid resistor value some to see if it stops the run away, or improves the tube performance, if you are inclined to tinkering with things.
I like the TS 6L6G but they are expensive, doubly so when half fail just sitting in the box ...
I don't know anything about Tube Depots bias point ratings. Without knowing how they get this data point, it seems rather meaningless.
Win W5JAG
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